//传入图片路径，返回base64
export function imgToBase64(file) {

  function getBase64Image(img, width, height) {//width、height调用时传入具体像素值，控制大小 ,不传则默认图像大小
    var canvas = document.createElement("canvas");
    canvas.width = width ? width : img.width;
    canvas.height = height ? height : img.height;

    var ctx = canvas.getContext("2d");
    ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
    var dataURL = canvas.toDataURL();
    return dataURL;
  }

  var image = new Image();
  image.crossOrigin = '';
  image.src = img;
  var deferred = $.Deferred();
  if (img) {
    image.onload = function () {
      deferred.resolve(getBase64Image(image));//将base64传给done上传处理
    }
    return deferred.promise();//问题要让onload完成后再return sessionStorage['imgTest']
  }
}
